Dependence of Ambipolar Transport on First Active Layer Thickness in Organic Homostructure Transistors

We investigated the dependence of ambipolar transport on the first active layer thickness in organic thin-film transistors based on an F 16 CuPc/CuPc homostructure. Ambipolar transport is observed at the first layer (F 16 CuPc) film thickness between 4 and 12 nm. By increasing the first layer thickness, n -channel operating characteristics are enhanced, whereas p -channel operating characteristics are suppressed. As a result, a balanced transport behavior is shown at the first layer thickness of 5 nm. When the first film thickness is larger than 12 nm, only the n -type operating characteristics are observed. The electron field-effect mobility is enhanced up to 2.6 × 10 -2 cm 2 V -1 s -1 and the threshold voltage is suppressed to -7.4 V. This result gives us a guide for improving the device performance of n -channel OTFTs employing an organic p n junction.